Translation:My father usually uses the credit card.
Your comments and observations are always very helpful and have allowed us to edit or even remove items. Even though we thought we had done a good review we've discovered many things that needed editing, as you will have noticed. So, in this case, you had me rushing off to the grammar books or rather sites and what I see is that while many adverbs come at the end of the sentence adverbs of frequency usually come before the main verb.
I've found several sources and here are two of the most reliable.
The Univ of Michigan: :https://www.press.umich.edu/pdf/9780472032426-unit5.pdf
and the British Council: http://learnenglishteens.britishcouncil.org/grammar-vocabulary/grammar-videos/adverbs-frequency
To cover both Am. Eng and Br. Eng. ;-)
I repeat your input has always been of great value and has helped avoid serious errors. We are all grateful and please keep your comments coming.
The placement of adverbs in English follows certain rules, putting usually after a verb that's not the verb to be is actually wrong: https://www.bbc.co.uk/learningenglish/spanish/course/lower-intermediate/unit-4/tab/grammar#
I understand that this is not ideal for people who learn through a language they may be more likely to make mistakes in, but it's not possible to create a course with a bank of answers that has mistakes in it. I hope you can see it as an opportunity to improve your English too while learning Greek! :)